Bring 6 cups of water to a boil in a large saucepan. Add shrimp, and cook 3 minutes or until done. Drain and rinse under cold running water. Peel shrimp, and chill.
Combine lemon juice, Dijon mustard, oil, water, salt, and pepper, and stir well.
Add chilled shrimp, pasta, cilantro, green onions, and carambola slices to lemon juice mixture, and toss gently to coat. Serve on lettuce-lined plates, if desired.